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Diel distribution of age-0 largemouth bass, Micropterus salmoides, in B. E. Jordan Lake, North Carolina (USA) and its relation to cover

We used prepositioned area electrofishers (PAEs, 10×1.5 m) to assess diel differences in distribution of age-0 largemouth bass, Micropterus salmoides , in August 1992–1993 in a paired sampling design. PAEs were placed parallel to shore in an embayment of an unvegetated reservoir (B. E. Jordan Lake, North Carolina, USA). The catch per unit effort (CPUE=fish/PAE) was significantly higher at night than during the day in both years, indicating that age-0 largemouth bass exhibit nocturnal inshore movements. Age-0 largemouth bass captured inshore during day were smaller than those captured at night, indicating that movement patterns may change ontogenetically. Inshore-offshore movements of age-0 largemouth bass were significantly reduced in the presence of cover, suggesting that diel movements were influenced by specific habitat components. Diel movements likely were related to foraging, resting and predator avoidance behavior and could affect population dynamics and introduce bias in assessment programs.

North Carolina↗

Annual Nutrient Loadings, Primary Productivity, and Trophic State of Lake Koocanusa, Montana and British Columbia, 1972-80

Limnological data collected at Lake Koocanusa were used to investigate the relationship of nutrient loadings, primary productivity, and trophic state of the reservoir during 1972-80. The reservoir, on the Kootenai River, was impounded by Libby Dam on March 21, 1972. Manipulation of the 7.16-cubic-kilometer reservoir for flood control, its primary function, created large fluctuations in reservoir volume and produced annual lake-filling times that ranged from 0.14 to 0.66 year. Loadings of nitrogen and phosphorus prior to and following impoundment of Lake Koocanusa were found to be large enough to predict eutrophic conditions. Beginning in 1976, total phosphorus loadings, but not total nitrogen loadings, were substantially reduced following improvements in waste-water treatment at a fertilizer plant located upstream from the reservoir. The closure of Libby Dam substantially reduced loadings of nitrogen and phosphorus downstream from Lake Koocanusa. On the average, the reservoir retained 63 percent of its influent loading of total phosphorus and 25 percent of its influent loading of total nitrogen. Daily areal and volumetric primary productivity varied widely in each year at four sampled limnological stations. During the 9 years studied, daily areal primary productivity, in milligrams of carbon fixed per square meter, ranged from 0.4 to 420.0; the mean of the 313 sampled days was 128.5. Annual areal primary productivity ranged from 23.2 to 38.5 grams of carbon fixed per square meter and thereby categorized Lake Koocanusa as oligotrophic. The relationship of annual areal primary productivity and 12 selected environmental variables was determined by multiple regression analysis. One of the models that was derived used two variables-annual euphotic zone depth and annual areal phosphorus loading-and accounted for 62.0 percent of the variation in annual areal primary productivity. The distribution of chlorophyll a within the water column indicated that, on the average, more than one-half of the phytoplankton in the reservoir was beneath the euphotic zone. These results support the hypothesis that the reservoir's weak thermal structure had allowed circulation of phytoplankton out of the euphotic zone. The trophic state of Lake Koocanusa was categorized as eutrophic when based on the relationship of the nutrient loadings and the reservoir's ratio of mean depth to hydraulic-residence time. This result conflicted with the oligotrophic ranking the reservoir received based on its areal primary productivity. The discrepancy in trophic state was attributed mainly to the failure of nutrient loading models to adequately account for physical processes within reservoirs. Part of the nutrient loading that entered Lake Koocanusa was unavailable to phytoplankton because the nutrients were carried beneath the euphotic zone by large volumes of interflow and underflow. Another part of the nutrient loading was adsorbed to suspended sediment and removed from the water column. Thus, phytoplankton primary productivity was controlled not only by nutrients, but also by other limno logical processes.

Professional Paper↗

Frameworks for amending reservoir water management

Managing water storage and withdrawals in many reservoirs requires establishing seasonal targets for water levels (i.e., rule curves) that are influenced by regional precipitation and diverse water demands. Rule curves are established as an attempt to balance various water needs such as flood control, irrigation, and environmental benefits such as fish and wildlife management. The processes and challenges associated with amending rule curves to balance multiuse needs are complicated and mostly unfamiliar to non-US Army Corps of Engineers (USACE) natural resource managers and to the public. To inform natural resource managers and the public we describe the policies and process involved in amending rule curves in USACE reservoirs, including 3 frameworks: a general investigation, a continuing authority program, and the water control plan. Our review suggests that water management in reservoirs can be amended, but generally a multitude of constraints and competing demands must be addressed before such a change can be realized.

Lake and Reservoir Management↗

Population estimate of Chinese mystery snail (Bellamya chinensis) in a Nebraska reservoir

The Chinese mystery snail ( Bellamya chinensis ) is an aquatic invasive species in North America. Little is known regarding this species’ impacts on freshwater ecosystems. It is believed that population densities can be high, yet no population estimates have been reported. We utilized a mark-recapture approach to generate a population estimate for Chinese mystery snail in Wild Plum Lake, a 6.47-ha reservoir in southeast Nebraska. We calculated, using bias-adjusted Lincoln-Petersen estimation, that there were approximately 664 adult snails within a 127 m2 transect (5.2 snails/m2). If this density was consistent throughout the littoral zone (<3 m in depth) of the reservoir, then the total adult population in this impoundment is estimated to be 253,570 snails, and the total Chinese mystery snail wet biomass is estimated to be 3,119 kg (643 kg/ha). If this density is confined to the depth sampled in this study (1.46 m), then the adult population is estimated to be 169,400 snails, and wet biomass is estimated to be 2,084 kg (643 kg/ha). Additional research is warranted to further test the utility of mark-recapture methods for aquatic snails and to better understand Chinese mystery snail distributions within reservoirs.

Nebraska↗

Temperature and oxygen in Missouri reservoirs

Vertical profiles of water temperature (n = 7193) and dissolved oxygen (n = 6516) were collected from 235 Missouri reservoirs during 1989–2007; most data were collected during May–August and provide a regional summary of summer conditions. Collectively, surface water temperature ranged from a mean of ~22 C in May to 28 C in July, and individual summer maxima typically were 28–32 C. Most (~95%) reservoirs stably stratify by mid-May, but few are deep enough to have hypolimnia with near-uniform temperatures. Among stratified reservoirs, maximum effective length and maximum depth accounted for 75% of the variation in mixed depth and thermocline depth. Ephemeral, near-surface thermoclines occurred in 39% of summer profiles and were most frequent in small, turbid reservoirs. Isotherms below the mixed layer deepen during stratification, and the water column is >20 C by August in all but the deepest reservoirs. Most reservoirs showed incipient dissolved oxygen (DO) depletion by mid-May, and by August, 80% of profiles had DO minima of <1 mg/L. Surface area and chlorophyll (Chl) explained 37% of variation in the earliest date of anoxia, and Chl explained >50% of variation in DO below the mixed layer during summer. Warm summer temperatures and widespread low DO often limit available fish habitat in Missouri reservoirs and compress warm-water fish communities into subsurface layers that exceed their thermal preferences. This study provides a regional baseline of reservoir temperature and oxygen conditions useful for future evaluations of eutrophication and the effects of a warming climate.

Missouri↗

Waterlogging in an alluvial aquifer near Lake Minnequa, Pueblo, Colorado

The Lake Minnequa area, located immediately south of the Arkansas River near Pueblo, Colo., is mantled with as much as 46 feet (14 meters) of alluvium covering bedrock of Pierre Shale and Niobrara Formation. Surface water enters the area by the Minnequa Canal and the St. Charles Flood Ditch. The water is stored in Lake Minnequa and other reservoirs. Seepage from St. Charles Reservoirs No. 2 and No. 3 is the major source of water to the alluvial aquifer. The depth of the water table ranges from 0 to 40 feet (0 to 12.2 meters). An 0.5-square-mile (1.3-square-kilometer) area immediately south of Lake Minnequa has a water table less than 6 feet (1.8 meters) below land surface. Lake Minnequa is the principal cause of the shallow water table and resulting waterlogged soil. The bedrock hill east of Lake Minnequa and ground-water flow also contribute to the problem. To eliminate the waterlogging problem, the water table would have to be at least 6 feet (1.8 meters) below land surface. Possible alternatives for eliminating the problem include lowering the water level in Lake Minnequa, placing a network of dewatering wells, or constructing a drainage system in the waterlogged area. (Woodard-USGS)

Colorado↗

Travel time for solutes, upper Sabine River basin, Texas, April 16-30, 1972

The U.S. Geological Survey, in cooperation with the Sabine River Compact Administration, conducted time-of-travel studies in the Sabine River Basin on April 16-30, 1972. One study was made on the main stem of the Sabine River in four reaches from Lake Tawakoni to Toledo Bend Reservoir, a distance of 219 miles. Two other studies were made on reaches of Lake Fork Creek and Big Sandy Creek. The purpose of these studies was to provide travel-rate data to be used by the Sabine River Authority of Texas in constructing a hydrologic model of the basin.

Texas↗

Physicochemical and analytical data for tributary water, lake water, and lake sediment, Lake Arrowhead, Clay and Archer Counties, Texas, 2006

Lake Arrowhead is a reservoir about 24 kilometers southeast of Wichita Falls, Texas, that provides drinking water for the city of Wichita Falls and surrounding areas. The U.S. Geological Survey, in cooperation with the City of Wichita Falls, did a study in 2006 to assess conditions contributing to elevated arsenic concentrations in Lake Arrowhead. This report describes the sampling and analytical methods, quality assurance, and physicochemical and analytical data. Physiochemical properties were measured in and water samples were collected from five tributaries to Lake Arrowhead (Little Wichita River, West Little Post Oak Creek, East Little Post Oak Creek, Deer Creek, and an unnamed tributary) immediately after storms. Lake water measuring and sampling were done approximately monthly from January through September 2006 at three deep-water sites and seasonally, in January and August 2006, at three shallow-water sites. Cores of lake bottom sediment were collected from five sites on August 30, 2006. Arsenic concentrations in tributary water samples ranged from 1.5 to 6.3 and 0.5 to 4.8 micrograms per liter for unfiltered and filtered samples, respectively. The highest arsenic concentrations were in samples collected from the West Little Post Oak Creek sampling site. Physicochemical properties in lake water varied with depth and season. Dissolved arsenite plus arsenate concentrations in lake water samples generally were between 3 and 5 micrograms per liter. Arsenite concentrations typically were below the laboratory reporting level of 0.6 microgram per liter. There were no detections of monomethylarsonate or dimethylarsinate. The concentration of arsenic in lake sediment samples ranged from 4.4 to 11.2 milligrams per kilogram, with a median of 6.4 milligrams per kilogram. The median arsenic concentration of the five top-interval sediment samples was 8.8 milligrams per kilogram, which generally is higher than the concentrations estimated to be on suspended sediment in the tributaries. Sediment concentrations of seven trace elements were compared to two consensus-based sediment quality guidelines for each: the threshold effect concentration and the probable effect concentration. Arsenic concentration exceeded the threshold effect concentration in one top-interval sediment sample.

Data Series↗

Environmental impacts of petroleum production: Fate of inorganic and organic chemicals in produced water from the Osage-Skiatook Petroleum Environmental Research sites, Osage County, Oklahoma

About 15 scientists from the U. S. Geological Survey, other Federal agencies and academia are involved in a multidisciplinary investigation to study the transport, fate, and natural attenuation of inorganic salts, trace metals, radionuclides and organic compounds present in produced water, and their impacts on soil, surface and ground water and the local ecosystem at the Osage-Skiatook Petroleum Environmental Research (OSPER) A and B sites, located in Osage County, OK. The Branstetter lease, OSPER B site, is typical of many aging petroleum fields in Osage County, which ranks among the top oil and gas producing counties in Oklahoma with close to 40,000 wells. Current production in Osage County is mainly from stripper wells (averaging ~2.8 bbls/d oil and >30 bbls/d brine) that are shallow, mostly 300-700 m in depth, and produce from several sandstones of Pennsylvanian age. About one hectare of land at the OSPER B site is affected by salt scarring, soil salinization and brine and petroleum contamination due to the leakage of produced water and associated hydrocarbons from two brine pits and due to accidental releases from active tank batteries. Eventually, the bulk of inorganic salts and some dissolved organic species in the released brine reach, directly or via the two local streams, the adjacent Skiatook Lake, a 4250-hectare reservoir that provides drinking water to the local communities and is a major recreational fishery. About 40 water samples were obtained from several oil wells at the B site and adjoining areas, the two brine pits, several brine pools and seeps in the impacted area, local streams, Skiatook Lake, and from about 20 boreholes (1-71 m deep), recently drilled and completed with slotted PVC tubing. Water level monitoring and additional sampling is continuing. Results to date show that the produced water is a high-salinity (~150,000 mg/L total dissolved solids) Na-Ca-Cl brine, with relatively high concentrations of Sr, Mg and NH4, but low amounts of SO4 and H2S. With the exception of Fe and Mn, the concentrations of trace metals are low, and the values of dissolved organics are relatively low. As the brine flows from the brine pits through the shallow eolian sand, colluvial and alluvial deposits to the streams and Skiatook Lake, it is diluted by infiltrating water from precipitation. Its chemical composition is modified by sorption, mineral precipitation/dissolution, transpiration, volatilization and oxidation/reduction reactions. Bacteria likely play an important role in many of these reactions.

Oklahoma↗

A rare Uroglena bloom in Beaver Lake, Arkansas, spring 2015

A combination of factors triggered a Uroglena volvox bloom and taste and odor event in Beaver Lake, a water-supply reservoir in northwest Arkansas, in late April 2015. Factors contributing to the bloom included increased rainfall and runoff containing increased concentrations of dissolved organic carbon, followed by a stable pool, low nutrient concentrations, and an expansion of lake surface area and littoral zone. This was the first time U. volvox was identified in Beaver Lake and the first time it was recognized as a source of taste and odor. Routine water quality samples happened to be collected by the US Geological Survey and the Beaver Water District throughout the reservoir during the bloom—. Higher than normal rainfall in March 2015 increased the pool elevation in Beaver Lake by 2.3 m (by early April), increased the surface area by 10%, and increased the littoral zone by 1214 ha; these conditions persisted for 38 days, resulting from flood water being retained behind the dam. Monitoring programs that cover a wide range of reservoir features, including dissolved organic carbon, zooplankton, and phytoplankton, are valuable in explaining unusual events such as this Uroglena bloom.

Arkansas↗

Introduction and summary of findings

Lakes Mead and Mohave, which are the centerpieces of Lake Mead National Recreation Area (LMNRA), provide many significant benefits that have made the modern development of the Southwestern United States possible. Lake Mead is the largest reservoir by volume in the nation and it supplies critical storage of water supplies for more than 25 million people in three Western States (California, Arizona, and Nevada). Storage within Lake Mead supplies drinking water and the hydropower to provide electricity for major cities including Las Vegas, Phoenix, Los Angeles, Tucson, and San Diego, and irrigation of more than 2.5 million acres of croplands (National Park Service, 2010). Lake Mead is arguably the most important reservoir in the nation because of its size and the services it delivers to the Western United States (Holdren and Turner, 2010).

Arizona, Nevada↗

Suspended-sediment loads, reservoir sediment trap efficiency, and upstream and downstream channel stability for Kanopolis and Tuttle Creek Lakes, Kansas, 2008-10

Continuous streamflow and turbidity data collected from October 1, 2008, to September 30, 2010, at streamgage sites upstream and downstream from Kanopolis and Tuttle Creek Lakes, Kansas, were used to compute the total suspended-sediment load delivered to and released from each reservoir as well as the sediment trap efficiency for each reservoir. Ongoing sedimentation is decreasing the ability of the reservoirs to serve several purposes including flood control, water supply, and recreation. River channel stability upstream and downstream from the reservoirs was assessed using historical streamgage information. For Kanopolis Lake, the total 2-year inflow suspended-sediment load was computed to be 600 million pounds. Most of the suspended-sediment load was delivered during short-term, high-discharge periods. The total 2-year outflow suspended-sediment load was computed to be 31 million pounds. Sediment trap efficiency for the reservoir was estimated to be 95 percent. The mean annual suspended-sediment yield from the upstream basin was estimated to be 129,000 pounds per square mile per year. No pronounced changes in channel width were evident at five streamgage sites located upstream from the reservoir. At the Ellsworth streamgage site, located upstream from the reservoir, long-term channel-bed aggradation was followed by a period of stability. Current (2010) conditions at five streamgages located upstream from the reservoir were typified by channel-bed stability. At the Langley streamgage site, located immediately downstream from the reservoir, the channel bed degraded 6.15 feet from 1948 to 2010. For Tuttle Creek Lake, the total 2-year inflow suspended-sediment load was computed to be 13.3 billion pounds. Most of the suspended-sediment load was delivered during short-term, high-discharge periods. The total 2-year outflow suspended-sediment load was computed to be 327 million pounds. Sediment trap efficiency for the reservoir was estimated to be 98 percent. The mean annual suspended-sediment yield from the upstream basin was estimated to be 691,000 pounds per square mile per year. In general, no pronounced changes in channel width were evident at six streamgage sites located upstream from the reservoir. At the Barnes and Marysville streamgage sites, located upstream from the reservoir, long-term channel-bed degradation followed by stability was indicated. At the Frankfort streamgage site, located upstream from the reservoir, channel-bed aggradation of 1.65 feet from 1969 to 1989 followed by channel-bed degradation of 2.4 feet from 1989 to 2010 was indicated and may represent the passage of a sediment pulse caused by historical disturbances (for example, channelization) in the upstream basin. With the exception of the Frankfort streamgage site, current (2010) conditions at four streamgages located upstream from the reservoir were typified by channel-bed stability. At the Manhattan streamgage site, located downstream from the reservoir, high-flow releases associated with the 1993 flood widened the channel about 60 feet (30 percent). The channel bed at this site degraded 4.2 feet from 1960 to 1998 and since has been relatively stable. For the purpose of computing suspended-sediment concentration and load, the use of turbidity data in a regression model can provide more reliable and reproducible estimates than a regression model that uses discharge as the sole independent variable. Moreover, the use of discharge only to compute suspended-sediment concentration and load may result in overprediction. Stream channel banks, compared to channel beds, likely are a more important source of sediment to Kanopolis and Tuttle Creek Lakes from the upstream basins. Other sediment sources include surface-soil erosion in the basins and shoreline erosion in the reservoirs.

Kansas↗

Hydrographic surveys of four narrows within the Namakan reservoir system, Voyageurs National Park, Minnesota, 2011

The U.S. Geological Survey performed multibeam echosounder hydrographic surveys of four narrows in the Namakan reservoir system in August 2011, in cooperation with the International Joint Commission and Environment Canada. The data-collection effort was completed to provide updated and detailed hydrographic data to Environment Canada for inclusion in a Hydrologic Engineering Centers River Analysis System hydraulic model. The Namakan reservoir system is composed of Namakan, Kabetogama, Sand Point, Crane, and Little Vermilion Lakes. Water elevations in the Namakan reservoir system are regulated according to rule curves, or guidelines for water-level management based on the time of year, established by the International Joint Commission. Water levels are monitored by established gages on Crane Lake and the outlet of Namakan Lake at Kettle Falls, but water elevations throughout the system may deviate from these measured values by as much as 0.3 meters, according to lake managers and residents. Deviations from expected water elevations may be caused by between-lake constrictions (narrows). According to the 2000 Rule Curve Assessment Workgroup, hydrologic models of the reservoir system are needed to better understand the system and to evaluate the recent changes made to rule curves in 2000. Hydrographic surveys were performed using a RESON SeaBat™7125 multibeam echosounder system. Surveys were completed at Namakan Narrows, Harrison Narrows, King Williams Narrows, and Little Vermilion Narrows. Hydrographic survey data were processed using Caris HIPS TM and SIPS TM software that interpolated a combined uncertainty and bathymetric estimator (CUBE) surface. Quality of the survey results was evaluated in relation to standards set by the International Hydrographic Organization (IHO) for describing the uncertainty of hydrographic surveys. More than 90 percent of the surveyed areas at the four narrows have resulting bed elevations that meet the IHO “Special Order” quality. Survey datasets published in this report are formatted as text files of x-y-z coordinates and as CARIS Spatial Archive TM (CSAR TM ) files with corresponding metadata.

Minnesota↗

Floods in the Canadian and Pecos River basins of New Mexico, May and June 1937

In May and June floods occurred in the Canadian and Pecos River Basins of New Mexico that were unusually high and in many places were record breaking. The floods were caused by heavy rains that occurred over the eastern part of the State from May 23 to June 4 in a series of intense and intermittent storms. During these storms of the cloudburst type as much as 12 inches of rain fell in the 13-day period, and a fall of 7 inches in 2 hours and 40 minutes was reported from the vicinity of Clayton. Heavy rains also fell in the mountainous region west of Roswell, amounting to as much as l0 inches at some places. Much of the region that had excessive rainfall is relatively flat and has no well-defined drainage system. From these areas there was very little run-off and practically no water was contributed to the major streams. Hail fell at many places in eastern New Mexico, causing damage to crops, livestock, and other property. Hail fell somewhere in the Canadian and Pecos River Basins almost every day during the storm period, but the duration of the fall was generally short. The largest hailstones were reported from Clayton, where one stone measured 8 inches in circumference and weighed 9 ounces; at Centerville, where reports state that some stones were 9 to 10 inches in circumference; and near Roswell, where it was reported that six stones would fill a gallon bucket. The Canadian River flood reached a peak at Logan of 110,000 second-feet, which has been exceeded in this century only by the floods of 1904, 1909, and 1914. The total run-off at Logan for the flood period has been computed as 653,800 acre-feet. At Santa Rosa the Pecos River reached a maximum discharge of 88,200 second-feet, which is greater than any previously recorded. This flood was partly stored in the Alamogordo Reservoir; the peak below the reservoir was only 25,200 second-feet. The Pecos River flood at Roswell reached a maximum discharge of more than 80,000 second-feet. This water came mostly from tributaries that have .their sources in the mountainous area west of Roswell. The Cienaga del Macho, ordinarily a small dry creek, discharged about 49,800 second-feet at its peak. The Rio Hondo experienced several flood peaks, the largest at Roswell probably being near 20,000 second-feet. Berrendo Creek, which enters the Rio Hondo near Roswell, had a computed peak discharge of 37,700 second-feet. Roswell was subjected to several floods that inundated large areas of the town. Considerable damage was done by the water, which covered nearly all the area occupied by the town. Lake McMillan, an artificial reservoir on the Pecos River about 12 miles above Carlsbad, was put to a severe strain by the large quantity of water passing through it, but no serious damage resulted. The capacity of the lake at spillway level is about 39,000 acre-feet, but at the peak of the flood the lake held about 86,000 acre-feet. The total quantity of water passing through the lake during the flood period was more than 440,000 acre-feet. This report presents data pertinent to the floods of May and June 1937, including results of peak discharge determinations made at about 14 miscellaneous places, records of peak stages and discharges and of mean daily discharges during the flood period at 23 regular river-measurement stations, records of rainfall at about 190 places, an isohyetal map showing rainfall over the entire State and two isohyetal maps showing rainfall over the Canadian and Pecos River Basins, and a discussion of the weather conditions during the flood period, including an upper-air wind and pressure chart of the United States for May 28, 1937. In addition to the information listed above the report includes a summary of records of past floods at all places in New Mexico at which authentic records were available.

New Mexico↗

Phytoplankton, taste-and-odor compounds, and cyanotoxin occurrence in four water-supply reservoirs in the Triangle area of North Carolina, April–October 2014

Prior to 2014, local utilities and State agencies monitored for cyanotoxins and taste-and-odor (T&O) compounds and reported occasional detections in three water-supply reservoirs in Wake County, North Carolina. Comparable data for cyanotoxins and T&O compounds were lacking for other water-supply reservoirs in the Triangle area of North Carolina. This report assesses whether cyanotoxins and T&O compounds occurred in four previously unmonitored North Carolina Triangle area water-supply reservoirs at levels that exceed existing North Carolina and U.S. Environmental Protection Agency recreational and drinking water health advisory, guidance, and criterion levels based on data collected during the peak phytoplankton growth period in 2014. Samples were collected from five sites across the study reservoirs (Cane Creek Reservoir, West Fork Eno River Reservoir, B. Everett Jordan Lake, and University Lake) between April and October 2014 and analyzed for physical characteristics, chemical constituents, phytoplankton communities, cyanotoxins, and T&O compounds. Lake stratification during the sampling period in 2014 could indicate that the deep zones of the water column, during stratified anoxic conditions, may serve as possible sources of nutrients and metals for algal growth and other biogeochemical processes. Differences in phytoplankton communities were attributed to variability in environmental conditions across the sites and sampling events. Differences generally were greater among sites than among sampling events for phytoplankton communities and environmental conditions. Phytoplankton community assemblages, within reservoirs, often were dominated by cyanobacteria that contained genera capable of producing T&O compounds and cyanotoxins during summer and fall months. The occurrence and associated biovolumes of potential producers of cyanotoxins and T&O compounds varied across the sites and sampling events. Of 20 samples collected during the study, the T&O compound geosmin and the cyanotoxin microcystin were present in 19 and 18 samples, respectively. While not harmful, the aesthetically displeasing geosmin concentrations periodically exceeded the human detection threshold of 15 nanograms per liter at most sites. The T&O compound 2-methylisoborneol (MIB) was detected in 11 of 20 samples, with concentrations below the human detection threshold of 15 nanograms per liter in all but one sample. The cyanotoxin anatoxin-a was detected in two of the samples. No other cyanotoxins were detected during the study. In general, results did not indicate the biovolume of any given phytoplankton genera in the study was correlated with increased concentrations of MIB, geosmin, or microcystin. Results from this study indicated that microcystin concentrations in the water-supply reservoirs in the Triangle area were below EPA-recommended recreational level of 8 micrograms per liter, but periodically exceeded the EPA finished-water 10-day health advisory level of 0.3 microgram per liter for bottle-fed infants and preschool-age children. This suggests longer term data collection may be necessary to better understand the magnitude and frequency of cyanotoxin concentrations in these four water-supply reservoirs, particularly those with an elevated risk of exceeding the EPA 10-day health advisory levels in the finished drinking water or those with a higher frequency of T&O compound occurrence.

North Carolina↗

A method for improving predictions of bed-load discharges to reservoirs

Effective management options for mitigating the loss of reservoir water storage capacity to sedimentation depend on improved predictions of bed-load discharges into the reservoirs. Most predictions of bed-load discharges, however, are based on the assumption that the rates of bed-load sediment availability equal the transport capacity of the flow, ignoring the spatio-temporal variability of the sediment supply. This paper develops a semiquantitative method to characterize bed-load sediment transport in alluvial channels, assuming a channel reach is non-supply limited when the bed-load discharge of a given sediment particle-size class is functionally related to the energy that is available to transport that fraction of the total bed-load. The method was applied to 22 alluvial stream channels in the USA to determine whether a channel reach had a supply-limited or non-supply-limited bed-load transport regime. The non-supply-limited transport regime was further subdivided into two groups on the basis of statistical tests. The results indicated the pattern of bed-load sediment transport in alluvial channels depends on the complete spectrum of sediment particle sizes available for transport rather than individual particle-size fractions represented by one characteristic particle size. The application of the method developed in this paper should assist reservoir managers in selecting bed-load sediment transport equations to improve predictions of bed-load discharge in alluvial streams, thereby significantly increasing the efficiency of management options for maintaining the storage capacity of waterbodies. ?? 2007 Blackwell Publishing Asia Pty Ltd.

Lakes and Reservoirs: Research and Management↗

How reservoirs alter drinking water quality: Organic matter sources, sinks, and transformations

Within reservoirs, production, transformation, and loss of dissolved organic matter (DOM) occur simultaneously. While the balance between production and loss determines whether a reservoir is a net sink or source of DOM, changes in chemical composition are also important because they affect DOM reactivity with respect to disinfection by-product (DBP) formation. The composition of the DOM pool also provides insight into DOM sources and processing, which can inform reservoir management. We examined the concentration and composition of DOM in San Luis Reservoir, a large off-stream impoundment of the California State Water Project. We used a wide array of DOM chemical tracers including dissolved organic carbon (DOC) concentration, trihalomethane and haloacetic acid formation potentials (THMFP and HAAFP, respectively), absorbance properties, isotopic composition, lignin phenol content, and structural groupings determined by 13 C nuclear magnetic resonance (NMR). There were periods when the reservoir was a net source of DOC due to the predominance of algal production (summer), a net sink due to the predominance of degradation (fall&ndash;winter), and balanced between production and consumption (spring). Despite only moderate variation in bulk DOC concentration (3.0&ndash;3.6 mg C/L), changes in DOM composition indicated that terrestrial-derived material entering the reservoir was being degraded and replaced by aquatic-derived DOM produced within the reservoir. Substantial changes in the propensity of the DOM pool to form THMs and HAAs illustrate that the DBP precursor pool was not directly coupled to bulk DOC concentration and indicate that algal production is an important source of DBP precursors. Results suggest reservoirs have the potential to attenuate DOM amount and reactivity with respect to DBP precursors via degradative processes; however, these benefits can be decreased or even negated by the production of algal-derived DOM.

California↗

Rhodhiss Lake, North Carolina: Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics, 1993-94

From January 1993 through March 1994, the U.S. Geological Survey conducted an investigation of Rhodhiss Lake in cooperation with the Western Piedmont Council of Governments. Objectives of the investigation were to describe ambient hydrologic and water-quality conditions, to estimate loadings of nutrients and suspended solids from selected tributaries and point sources, and to simulate hydraulic circulation and water-quality characteristics in Rhodhiss Lake using a hydrodynamic computer model. The riverine headwaters of Rhodhiss Lake were unstratified, well oxygenated, and contained relatively high concentrations of suspended solids and nutrients throughout the study period. In general, concentrations of suspended solids, nitrate, orthophosphate, and total phosphorus decreased in a downstream direction from the headwaters to the Rhodhiss Dam. However, increases in specific conductance frequently were observed downstream from a wastewater discharge near mid-reservoir. From mid-reservoir to the dam, Rhodhiss Lake thermally stratified during the summer of 1993. In this reach, dissolved oxygen was rapidly depleted from the bottom waters beginning in May 1993, and anoxic conditions persisted in the hypolimnion through the summer. During summer stratification, concentrations of nitrite plus nitrate, ammonia, and orthophosphate were low in the epilimnion, but concentrations of ammonia, orthophosphate, and total phosphorus increased in the hypolimnion. During fall and winter, Rhodhiss Lake was characterized by alternating periods of stratification and mixing. A maximum chlorophyll-a concentration of 52 micrograms per liter was observed at mid-reservoir on November 17, 1993, and was the only value that exceeded the North Carolina water-quality standard of 40 micrograms per liter. Concentrations of fecal coliform bacteria exceeded 200 colonies per 100 milliliters in the headwaters of Rhodhiss Lake 37 percent of the time, and at mid-reservoir and in the forebay 16 percent of the time. In Lower Creek, a tributary to Rhodhiss Lake, concentrations of fecal coliform bacteria exceeded 200 colonies per 100 milliliters in 76 percent of the samples. This stream also contained elevated concentrations of nitrite plus nitrate, phosphorus, and specific conductance. Loading estimates showed that almost all of the suspended solids and the majority of the nitrogen and phosphorus entering the headwaters of Rhodhiss Lake originated from nonpoint sources. During the investigation, point sources accounted for less than 1 percent of the suspended solids load to the reservoir headwaters, but point sources accounted for up to 27 and 22 percent of the total nitrogen and total phosphorus loads, respectively. Additional loadings of nitrogen and phosphorus entered Rhodhiss Lake by municipal wastewater discharge near mid-reservoir. The U.S. Army Corps of Engineers CE-QUAL-W2 model is a two-dimensional, laterally averaged model that simulates hydrodynamics and water quality. The model was applied to Rhodhiss Lake from Huffman Bridge to Rhodhiss Dam--a distance of 18.5 kilometers--and was calibrated using data collected from April 1993 through March 1994. During the simulation period, measured water levels varied a total of 1.32 meters, and water temperatures ranged from 4 to 30 degrees Celsius. The calibrated model provided good agreement between measured and simu- lated water levels at Rhodhiss Dam. Likewise, simulated water temperatures were generally within 2 degrees Celsius of measured values; however, the model tended to overpredict temperatures near the bottom of the reservoir by 1 to 3 degrees Celsius during warm months. This suggests that the model, as calibrated, overpredicts vertical mixing. Simulated dissolved oxygen concentrations followed the same general patterns and magnitudes as measured values, and there was good agreement between simulated and measured frequency of occurrence of dissolved oxygen concentrations less than 5 milligra

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